The present disclosure relates to a semiconductor structure and a method of forming the same. More particularly, the present disclosure relates to a semiconductor structure having a well-controlled extension profile and a method of forming the same.
As semiconductor devices shrink in each generation of semiconductor technology, it is more desirable to achieve step-function like source/drain extension profiles and high doping concentrations (on the order of 1021 atoms/cm3 or greater) for better device performance as well as process control. By “step-like source/drain extension profiles” it is meant to be atomically or near-atomically abrupt doping transitions.
Typical source/drain extension profiles formed by ion implantation or atomic layer doping are now insufficient. Ion implantation is difficult to control a junction depth below 10 nm and the junction depth is highly dependent on thermal diffusion, while atomic layer doping requires a long drive-in path and usually afterwards the dopant-profile will lose its abruptness. Moreover, any additional thermal processing which is performed after the formation of the source/drain extensions can further decrease the profile abruptness.
There is thus a need to provide a method to improve and control the extension profile, which is compatible to device scaling.